1 MEN Chameleon Bus
2 =================
3 4Table of Contents
5=================
61 Introduction
7 1.1 Scope of this Document
8 1.2 Limitations of the current implementation
92 Architecture
10 2.1 MEN Chameleon Bus
11 2.2 Carrier Devices
12 2.3 Parser
133 Resource handling
14 3.1 Memory Resources
15 3.2 IRQs
164 Writing an MCB driver
17 4.1 The driver structure
18 4.2 Probing and attaching
19 4.3 Initializing the driver
20 21 221 Introduction
23===============
24 This document describes the architecture and implementation of the MEN
25 Chameleon Bus (called MCB throughout this document).
26 271.1 Scope of this Document
28---------------------------
29 This document is intended to be a short overview of the current
30 implementation and does by no means describe the complete possibilities of MCB
31 based devices.
32 331.2 Limitations of the current implementation
34----------------------------------------------
35 The current implementation is limited to PCI and PCIe based carrier devices
36 that only use a single memory resource and share the PCI legacy IRQ. Not
37 implemented are:
38 - Multi-resource MCB devices like the VME Controller or M-Module carrier.
39 - MCB devices that need another MCB device, like SRAM for a DMA Controller's
40 buffer descriptors or a video controller's video memory.
41 - A per-carrier IRQ domain for carrier devices that have one (or more) IRQs
42 per MCB device like PCIe based carriers with MSI or MSI-X support.
43 442 Architecture
45===============
46 MCB is divided into 3 functional blocks:
47 - The MEN Chameleon Bus itself,
48 - drivers for MCB Carrier Devices and
49 - the parser for the Chameleon table.
50 512.1 MEN Chameleon Bus
52----------------------
53 The MEN Chameleon Bus is an artificial bus system that attaches to a so
54 called Chameleon FPGA device found on some hardware produced my MEN Mikro
55 Elektronik GmbH. These devices are multi-function devices implemented in a
56 single FPGA and usually attached via some sort of PCI or PCIe link. Each
57 FPGA contains a header section describing the content of the FPGA. The
58 header lists the device id, PCI BAR, offset from the beginning of the PCI
59 BAR, size in the FPGA, interrupt number and some other properties currently
60 not handled by the MCB implementation.
61 622.2 Carrier Devices
63--------------------
64 A carrier device is just an abstraction for the real world physical bus the
65 Chameleon FPGA is attached to. Some IP Core drivers may need to interact with
66 properties of the carrier device (like querying the IRQ number of a PCI
67 device). To provide abstraction from the real hardware bus, an MCB carrier
68 device provides callback methods to translate the driver's MCB function calls
69 to hardware related function calls. For example a carrier device may
70 implement the get_irq() method which can be translated into a hardware bus
71 query for the IRQ number the device should use.
72 732.3 Parser
74-----------
75 The parser reads the first 512 bytes of a Chameleon device and parses the
76 Chameleon table. Currently the parser only supports the Chameleon v2 variant
77 of the Chameleon table but can easily be adopted to support an older or
78 possible future variant. While parsing the table's entries new MCB devices
79 are allocated and their resources are assigned according to the resource
80 assignment in the Chameleon table. After resource assignment is finished, the
81 MCB devices are registered at the MCB and thus at the driver core of the
82 Linux kernel.
83 843 Resource handling
85====================
86 The current implementation assigns exactly one memory and one IRQ resource
87 per MCB device. But this is likely going to change in the future.
88 893.1 Memory Resources
90---------------------
91 Each MCB device has exactly one memory resource, which can be requested from
92 the MCB bus. This memory resource is the physical address of the MCB device
93 inside the carrier and is intended to be passed to ioremap() and friends. It
94 is already requested from the kernel by calling request_mem_region().
95 963.2 IRQs
97---------
98 Each MCB device has exactly one IRQ resource, which can be requested from the
99 MCB bus. If a carrier device driver implements the ->get_irq() callback
100 method, the IRQ number assigned by the carrier device will be returned,
101 otherwise the IRQ number inside the Chameleon table will be returned. This
102 number is suitable to be passed to request_irq().
103 1044 Writing an MCB driver
105=======================
106 1074.1 The driver structure
108-------------------------
109 Each MCB driver has a structure to identify the device driver as well as
110 device ids which identify the IP Core inside the FPGA. The driver structure
111 also contains callback methods which get executed on driver probe and
112 removal from the system.
113 114 115 static const struct mcb_device_id foo_ids[] = {
116 { .device = 0x123 },
117 { }
118 };
119 MODULE_DEVICE_TABLE(mcb, foo_ids);
120 121 static struct mcb_driver foo_driver = {
122 driver = {
123 .name = "foo-bar",
124 .owner = THIS_MODULE,
125 },
126 .probe = foo_probe,
127 .remove = foo_remove,
128 .id_table = foo_ids,
129 };
130 1314.2 Probing and attaching
132--------------------------
133 When a driver is loaded and the MCB devices it services are found, the MCB
134 core will call the driver's probe callback method. When the driver is removed
135 from the system, the MCB core will call the driver's remove callback method.
136 137 138 static init foo_probe(struct mcb_device *mdev, const struct mcb_device_id *id);
139 static void foo_remove(struct mcb_device *mdev);
140 1414.3 Initializing the driver
142----------------------------
143 When the kernel is booted or your foo driver module is inserted, you have to
144 perform driver initialization. Usually it is enough to register your driver
145 module at the MCB core.
146 147 148 static int __init foo_init(void)
149 {
150 return mcb_register_driver(&foo_driver);
151 }
152 module_init(foo_init);
153 154 static void __exit foo_exit(void)
155 {
156 mcb_unregister_driver(&foo_driver);
157 }
158 module_exit(foo_exit);
159 160 The module_mcb_driver() macro can be used to reduce the above code.
161 162 163 module_mcb_driver(foo_driver);
164